The present invention relates in general to a torque-responsive pressure mechanism in a ball-type planetary gear set.
From GE Pat. No. 2,136,243 a ball-type planetary gear set with a torque-controlled pressure mechanism is known. This prior-art device includes a fixed housing supporting for rotation a first shaft on which two mutually shiftable races provided with raceways for receiving planetary balls, are arranged. A second shaft supported in the housing in alignment with the first shaft carries for joint rotation another race with outer raceway which engages from above the planetary balls. Another rotatable outer race is arranged opposite the rotary outer race to engage the planetary balls from the opposite sides, whereby its position is axially adjustable by means of the pressure device. The pressure device couples one of the races with inner raceway to the first shaft. The opposite race with the inner raceway is rigidly connected to the first shaft, whereby the pressure device, which includes a pressure disk rigidly connected to the first shaft and engaging rolling bodies which cooperate with a raceway formed on the face of an axially shiftable race which is supported for free rotation on the first shaft. In this prior-art device, the pressure disk is in the form of an axial cam ring which generates the required compressing forces.
The disadvantage of this known device is the fact that the pitch angle of the cams relative to the base plane must be smaller than the angle of internal friction between the rolling bodies and the corresponding race. On the other hand, the lower limit of the pitch angle of the cams is determined by the largest permissible axial forces. Since the angle of friction depends both on the used materials of respective functional elements and on the condition of their contact surfaces, as well as on the employed lubricating agent, the operative conditions of the device are not well defined. It has been found from experience that, if this prior-art device is subject to torsional shocks resulting for instance during the start at full load or in driving oscillatory masses, the rolling bodies create depressions in the camming surfaces. Furthermore, even minute local plastic deformations suffice to make the device inoperative. Another disadvantage of prior-art devices of this kind is the fact that at low torsions the pressure device tends to rattle because the corresponding functional elements under this operational condition cease to positively engage.